Physiological stress levels in wild koala sub-populations facing anthropogenic induced environmental trauma and disease

Edward Narayan

doi:10.1038/s41598-019-42448-8

Abstract

Australian small mammals such as koalas must cope with immense pressure from anthropogenic induced stressors or trauma such as bushfires, vehicle collision impacts and habitat disturbance and land clearance. In addition, they must cope with diseases such as chlamydia. To date, there is no published literature on physiological stress levels in wild koala populations compared with identified environmental stressors. This study investigated physiological stress levels within sub-populations of wild koalas encountering environmental trauma and disease from New South Wales (NSW), Queensland (QLD) and South Australia (SA). Physiological stress was determined using a faecal glucocorticoid (or cortisol) metabolites (FGMs) enzyme-immunoassay (EIA) from 291 fresh faecal samples collected from wild koalas at the point of rescue. A healthy breeding sub-population from a forest reserve in QLD acted as a control group. Clearance of prime Eucalyptus habitat had the largest impact on FGMs, followed by bushfire related factors (e.g. flat demeanour, dehydration and burns injury). Koalas with other sources of physical injury (dog-attacks and vehicle collisions) and disease (chlamydia) also had higher FGMs compared to healthy wild koalas. Healthy wild koalas expressed the lowest median levels of FGMs. Overall, the results highlight that anthropogenic-induced stressors tend to increase physiological stress in wild koalas. Thus, the ultimate stressors such as habitat clearance and bush fire events could increase the incidences of proximate stressors such as dog attacks and vehicle collisions, and increase risks of foliage shortage, diseases and mortality. Therefore, there is need for ecological monitoring, conservation management actions and policy changes to curb the koala population crisis, especially within on-going and future land and road development programs.

Highlights

Australian wildlife have shown unique survival adaptations to prolonged drought and extreme temperature events[1], which include decreased metabolism[2,3,4], behavioural hiding/movement strategies[5,6], smaller body size for efficient heat dissipation[7,8], crepuscular activity and insulating covering[9]
Most recent ecological analyses conducted on the drivers of koala decline highlighted that disease and habitat change were two of the major factors influencing koala ecology, the researchers highlighted that no published study has demonstrated levels of physiological stress generated in wild koalas due to land clearance[23]
Highest median faecal glucocorticoid (or cortisol) metabolites (FGMs) levels (Table 1) was recorded for koalas sampled from land clearance area (105.9 ng/g) followed by found flat on the ground (88.50 ng/g), dehydration (83 ng/g), burns from bushfires (76 ng/g), vehicle collision (30.5 ng/g), dog attack (26 ng/g) and injury (16 ng/g)

Summary

Introduction

Australian wildlife have shown unique survival adaptations to prolonged drought and extreme temperature events[1], which include decreased metabolism[2,3,4], behavioural hiding/movement strategies[5,6], smaller body size for efficient heat dissipation[7,8], crepuscular activity and insulating covering[9]. Davies et al (2013) have shown that climate events as seen in south-western Queensland have affected koalas living in the edge of their distribution, where there was an 80% decline in numbers between 1995 and 2009 due to drought[9] These studies projected that koalas may cope poorly with extreme environment changes such as bushfires and land clearing[9,17]. Researchers have predicted, using bioclimatic modelling[23], that the current range of the koala will contract eastwards and southwards This will push koalas into areas where the existing population is already under pressure from threats that imposed by human development, for example, vehicle collisions and dog attacks

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